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Advancements in ferroic materials center upon understanding domain structures and their boundaries. This study innovates by directing the growth of lead halide perovskite microcrystals from the gas phase onto pre‐chosen substrates, thereby inducing an interfacial strain that prompts ferroelasticity‐driven structural transformation. A method of ferroelastic engineering in vapor‐grown perovskite heterostructures is thus unveiled, revealing ordered domain patterns of bright crystals with contrasting electro‐optical properties. In the case of the frustrated halide perovskite crystals, the strain is relaxed by the formation of alternating crystallographic twin domains. In the demonstrated orthorhombic system, these domains alternate between (110) and (002) orientation, with a (112) domain boundary. Perovskite ferroelastic effect with facet stability is correlated, attributed to the exposure of lower surface energy terminations, promoting the material's stability and efficiency. This findings result from direct electrical measurements, which pave the way for the tailored design of ferroic materials, optimizing their optoelectronic characteristics for enhanced device performance. [ABSTRACT FROM AUTHOR]

Radiation detection is being revolutionized by integrating photonic elements into scintillators. In this study, a scalable and cost‐effective method is proposed to achieve tuneable emission enhancement across the visible spectrum by colloidal self‐assembly of photonic crystals on scintillator surfaces. This concept is demonstrated for Eu3+/Tb3+‐doped Gd and Ta oxides. Widely available and affordable colloidal nanospheres of SiO2 or polymethyl methacrylate are self‐assembled on these scintillators. The size of the nanospheres is carefully optimized to match the desired emission lines of Eu3+/Tb3+. The result is homogeneous and closely‐packed structures with clear photonic bandgap in the visible range. Under X‐ray excitation, the scintillators covered with the photonic layers exhibit enhanced light extraction in the direction perpendicular to the surface, compared to isotropic emission in the bare scintillator. Such scintillation directionality, when optically matched with a proper detector, will result in higher efficiency of the overall detection system. Moreover, X‐ray imaging demonstrates an enhancement of 25% in system resolution of the scintillator supplemented with the photonic layer compared to unmodified scintillators. The proposed method is scintillator‐ and nanosphere‐agnostic, thus offering a promising versatile approach for directing the scintillation light toward a photodetector and increasing detection system performance, including high‐resolution imaging applications. [ABSTRACT FROM AUTHOR]

Scintillation materials convert high-energy radiation to optical light through a complex multistage process. The last stage of the process is spontaneous light emission, which usually governs and limits the scintillator emission rate and light yield. For decades, scintillator research focused on developing faster-emitting materials or external photonic coatings for improving light yields. Here, we experimentally demonstrate a fundamentally different approach: enhancing the scintillation rate and yield via the Purcell effect, utilizing optical environment engineering to boost spontaneous emission. This enhancement is universally applicable to any scintillating material and dopant when the material's nanoscale geometry is engineered. We design a thin multilayer nanophotonic scintillator, demonstrating Purcell-enhanced scintillation with 50% enhancement in emission rate and 80% enhancement in light yield. The emission is robust to fabrication disorder, further highlighting its potential for x-ray applications. Our results show prospects for bridging nanophotonics and scintillator science toward reduced radiation dosage and increased resolution for high-energy particle detection. [ABSTRACT FROM AUTHOR]

Collective optical properties can emerge from an ordered ensemble of emitters due to interactions between the individual units. Superlattices of halide perovskite nanocrystals exhibit collective light emission, influenced by dipole-dipole interactions between simultaneously excited nanocrystals. This coupling changes both the emission energy and rate compared to the emission of uncoupled nanocrystals. We demonstrate how quantum confinement governs the nature of the coupling between the nanocrystals in the ensemble. The extent of confinement is modified by controlling the nanocrystal size or by compositional control over the Bohr radius. In superlattices made of weakly confined nanocrystals, the collective emission is red-shifted with a faster emission rate, showing the key characteristics of superfluorescence. In contrast, the collective emission of stronger quantum-confined nanocrystals is blue-shifted with a slower emission rate. Both types of collective emission exhibit correlative multiphoton emission bursts, showing distinct photon bunching emission statistics. The quantum confinement changes the preferred alignment of transition dipoles within the nanocrystal and switches the relative dipole orientation between neighbors, resulting in opposite collective optical behaviors. Our results extend these collective effects to relatively high temperatures and provide a better understanding of exciton interactions and collective emission phenomena at the solid state.

Perovskite nanocrystal superlattices (NC SLs), made from millions of ordered crystals, support collective optoelectronic phenomena. Coupled NC emitters are highly sensitive to the structural and spectral inhomogeneities of the NC ensemble. Free electrons in scanning electron microscopy (SEM) are used to probe the cathodoluminescence (CL) properties of CsPbBr 3 SLs with a ∼20 nm spatial resolution. Correlated CL-SEM measurements allow for simultaneous characterization of structural and spectral heterogeneities of the SLs. Hyperspectral CL mapping shows multipole emissive domains within a single SL. Consistently, the edges of the SLs are blue-shifted relative to the central domain by up to 65 meV. We discover a relation between NC building block colloidal softness and the extent of the CL shift. Residual uniaxial compressive strains accompanying SL formation are contributors to these emission shifts. Therefore, precise control over the colloidal softness of the NC building blocks is critical for SL engineering.